Tuesday, November 17, 2009

I appreciate projects that are simple, can actually be made using novel technologies and which really work well for the task at hand. Among them are those that try and see if pedal power can be applied in any fashion to solving practical problems, however outrageous they maybe. And there should be solid reasons behind choosing pedal power.

Now PlasmaCAM Cutting Systems is a Colorado based company that markets an automated CNC cutter. This is a robotic cutting tool which is touted as being more versatile and more accurate than a plasma torch, achieving metal cutting accuracies as high as plus or minus five thousandths of an inch.

If you'll look, one PlasmaCAM project highlighted on their website is an interesting cable car, but a pedal powered one at that! The machine was made in the backyard of Colorado inventor Jason Bailey. All the parts that go into this "bike" was cut using PlasmaCAM in a few hours, which makes this a great application case study for the company.

Jason's dream was to make a cable car that could cross a 100 foot high cliff to the other side across the wide canyon. The design problem was being able to make a very simple and quiet machine for a flat crossing which would be powered by two people and could run in either direction. Both passengers would have to have a clean sensation with surroundings while crossing instead of being provided with a traveling experience polluted by the noise from motorized transport.

Being a pilot, he knew exactly what the disgusting sensation was of being enclosed in a noisy cabin as it powered you through the air with engine power. This motivated him to adapt pedal power to the cable car. The experience would be like riding a bike down the street of your neighborhood, except your roads in this case would be simply thin air between cliffs, 125 feet high above a stream at the bottom!

The computer depiction of the design aptly named Skybike

So he began building this bike out of plasma cut plates attached to pieces of square tubing. Bearings, sprockets and other drive parts would come from an old catalog and an old bike. The seats were made from 9/16 inch-plywood that was covered with foam rubber and seat covers stapled to the plywood. The seats could be quickly pivoted for travel in the opposite direction and they would be given custom made seat belts with aerospace quality buckles. The pedal position would also be adjustable.

Now the most important part.

Knowing that he would have a live car weight of 500 pounds, Bailey's math led him to use a 450 long, 250 pound stainless steel cable of 1/2 inch diameter. A hydraulic tensioner was used to test the cable at 22,000 pounds before each use. A portable air-compressor powered rock drill was used to dig deep into the rock, as far as 5 feet! Then, multiple expanding anchors were used to tie the cable into the bedrock. Finally, tripod supports were built out of 2-inch by 3/16-inch-thick square tubing to take as much as 5000 pounds of down force at the peak cable tension during testing. The cable pulleys would be located on these supports at what would be a perfect resting height for the bike on the cliff.

For the operating conditions of 500 pounds live weight at a cable tension of 14,000 pounds, Jason calculated that the cable would sag 4 feet in the middle of the canyon. See source.

How he got the cable between the two ends of the cliffs is the highlight of the story. Below, he describes this strenuous feat in his own words :

"People often ask how I got the cable across the canyon. It was no small feat, as the entire cable weighs about 250 pounds. I started by rolling the entire spool down to the bottom of the canyon. Next I lowered a 150-foot climbing rope down from the top of the cliff. With the bottom of the rope clamped to the end of the cable, I pulled the rope back up the cliff from the top while the cable was unwound. The last bit of cable was difficult to pull up because it became so heavy. I was barely able to get the end of it wrapped around a tree and clamped.

I dragged the other end of the cable back up the slope while the cable was untangled. I wrapped it around a tree at the top and clamped it as well. I used a hand-cable-winch and many pairs of locking pliers to gradually reel in more of the cable to the trees I was using at both sides of the canyon. I attached the climbing rope to the middle of the cable so I could work it up through the trees as it raised. This proved difficult, because the cable got caught in so many tree branches. One tree was especially large and stood right in the final path of where the cable needed to go. With the ends of the cable merely wrapped around trees, I actually rode the skybike out to the big tree and sawed the top of it off, about 100 feet off the ground."

Check out his full, amazing design report here which contains all the specifics of this project. He writes in the end that the skybike has become a popular local attraction, and people from all over the country have stopped by just to experience an exciting ride. It looks pretty breathtaking from the video below. If only I would have a chance to ride it...